1. Field of the Invention
This invention relates to a process for reactivating certain catalyst compositions comprising crystalline materials which have been steam-deactivated, said method involving the sequential steps of contacting said deactivated catalyst composition with a metal salt solution followed by contacting the metal salt solution contacted composition with a solution comprising a hydrogen ion precursor.
2. Description of Prior Art
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline alumminosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline aluminosilicates. These aluminosilicates can be described as a rigid three-dimensional framework of SiO.sub.4 and Al0.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total aluminum and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of aluminum to the number of various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given aluminosilicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. The zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite A (U.S. Pat. No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4 (U.S. Pat. No. 3,314,752), zeolite ZSM-5 (U.S. Pat. No. 3,702,886), zeolite ZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U.S. Pat. No. 3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983), ZSM-35 (U.S. Pat. No. 4,016,245), ZSM-38 (U.S. Pat. No. 4,046,859), and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.
The silicon/aluminum atomic ratio of a given zeolite is often variable. For example, zeolite X can be synthesized with silicon/aluminum atomic ratios of from 1 to 1.5; zeolite Y, from 1.5 to about 3. In some zeolites, the upper limit of the silicon/aluminum atomic ratio is unbounded. ZSM-5 is one such example wherein the silicon/aluminum atomic ratio is at least 2.5 and up to infinity. U.S. Pat. No. 3,941,871 (U.S. Pat. No. Re. 29,948) discloses a porous crystalline silicate made from a reaction mixture containing no deliberately added aluminum in the recipe and exhibiting the X-ray diffraction pattern characteristic of ZSM-5 type zeolites. U.S. Pat. Nos. 4,061,724, 4,073,865 and 4,104,294 describe crystalline silicas of varying aluminum and metal content.
The reactivation of steam-deactivated catalysts comprising zeolites has been a prime objective of the petrochemical and refining industries. The importance of catalysts comprising zeolites having a high silicon/aluminum atomic ratio, e.g. greater than about 3.5, in the petrochemical industry, and the likelyhood of such catalysts being deactivated by steam contact, makes their reactivation following steam deactivation especially important. In contrast to coke-deactivated catalysts which can be readily regenerated by air oxidation, no adequate technique has been heretofore developed for reactivation of steam-deactivated catalysts. Steam deactivation apparently involves removal of aluminum from zeolitic framework, a result which until now has been believed to be largely irreversible. The present method provides a convenient way to reactivate steam-deactivated catalysts. This will prove to be useful and, in fact, valuable in numerous process applications.
It is noted that U.S. Pat. Nos. 3,354,078 and 3,644,220 relate to treating crystalline aluminosilicates with volatile metal halides, including aluminum chloride. Neither of these latter patents is, however, concerned with treatment of catalysts comprising zeolites, especially zeolites having initially a high silicon/aluminum atomic ratio, which have been deactivated by contact with steam.
Various methods for regeneration of coke-deactivated catalysts comprising zeolites with a silicon/aluminum atomic ratio of less than 3.5 are exemplified by the methods taught in U.S. Pat. Nos. 3,493,490; 3,835,030; 4,085,069 and 4,268,376. A siliceous cracking catalyst comprised of naturally occurring clays or synthetically prepared composites such as silica-alumina having been coke-deactivated may be regenerated by the method taught in U.S. Pat. No. 2,814,598.
U.S. Pat. No. 3,684,738 teaches a method for reactivating a coke-deactivated catalyst comprising a crystalline aluminosilicate characterized by a silica/alumina mole ratio of greater than about 6 and a pore size of from about 5 to 13 angstroms. The method of the latter patent involves the sequential steps of burning the coke from the catalyst, contacting the catalyst with an ammonium chloride solution under specified conditions, washing the catalyst with water, air drying and then calcining the catalyst.
Other methods for reactivating spent catalysts include those taught in U.S. Pat. Nos. 3,533,959; 2,635,080; 4,055,482; 4,107,031; 4,139,433; 4,219,441; 2,981,676; 3,692,692; 3,835,028; 2,752,289 and 2,842,503. U.S. Pat. No. 3,533,959 teaches a method for reactivation of aluminosilicate catalyst which has lost activity by exposure to heat or steam which involves contact with a cation-containing agent capable of chelating with aluminum at a pH between 7 and 9. U.S. Pat. No. 2,635,080 discloses reactivating a platinum-containing alumina catalyst by treating same with a solution of metal nitrate and metal chloride, while U.S. Pat. Nos. 4,055,482; 4,107,031 and 4,139,433 generally disclose reactivation of zeolite catalysts by treatment with ammonia solutions. U.S. Pat. No. 4,219,441 discloses reactivation of zeolite catalyst by contact with alkali or alkaline earth metal ions.
Further methods are exemplified by U.S. Pat. Nos. 4,190,553 and 4,043,938. The former patent discloses the sequential steps of contacting a coke-deactivated catalyst with ammonium hydroxide and then with an aqueous ammonium salt solution. The latter patent discloses reactivating zeolites by contact with a bivalent metal salt solution followed by treatment with ammonia gas (having a small water content). The ammonia gas is taught to serve as a drying agent with essentially no bivalent metal replacement taking place.